Techniques for detecting a face in a captured image are widely used in various fields. For instance, the techniques are used for a digital camera to mark a face part in an image displayed on a preview screen. Or, by using the techniques, a face of a driver is monitored to automatically sound an alarm when the driver dozes off while driving.
According to a related art, for detecting facial features, e.g., eyes, nose, mouth, and ears, in a captured image, concerned areas which are considered to include facial features are conjectured, and characteristics of facial features, e.g., the fact that eyes are two and located on an upper part of a face, are used.
However, according to the above-described related art, facial features may not be effectively detected when a condition of taking an image is changed, or a direction of an image is changed.